Carla Pincombe's first instinct after giving birth seven weeks ago was not to hold the baby.

"I just wanted to see the boys cuddling her," she says.

For Andy and Simon, that moment marked the end of an emotional five-year rollercoaster ride that saw them travel around the world and spend tens of thousands of dollars.

At home in Heathmont last week, Carla, 37, cradles baby Adaline while her proud dads watch on. When asked about the birth the trio reply in near perfect unison: March 29, 5.02am, 3.7 kilograms.

Carla is among a growing number of women in Victoria who are deciding to become surrogates. "Its not something I would just do for anybody," she says, "but we developed a close friendship over time."

About 50 women agreed to be surrogates between 2010 and 2015, but in the last two years that figure has more than doubled. Of the 112 women who have become surrogates over the past seven years, 13 have carried two babies and one woman has carried three.

Sam Everingham, from Families Through Surrogacy, said Australian couples were increasingly turning to home since countries like India and Thailand clamped down on surrogacy laws.

"There has been an enormous shift in interest," he said. "Six years ago maybe five per cent of people were engaging in Australia and nowadays we're probably seeing 20 or 30 per cent."

But Mr Everingham said due to strict laws in Australia most couples were still eventually forced to go offshore.

Altruistic surrogacy is legal in every state in Australia except the Northern Territory. While it is illegal for a person to pay for sperm, eggs or surrogacy, reasonable expenses in surrogacy arrangements can be covered.

One of those couples is Andy Brough and Simon Curtis. The were trying to have a baby for five years before they met Carla. They had a surrogate in India, but she miscarried at 21 weeks and, when they went to try again, the Indian government changed the law to restrict surrogacy to heterosexual couples.

Back home, Andy's sister-in-law offered to be their surrogate using donor eggs, but they stopped after two failed IVF transfers. That's when the egg donor, Carla, offered to carry for them using her own eggs.

She has three daughters under 10 and wasn't planning to have any more children. But she loved her pregnancies and after meeting the couple as their donor she formed a close bond with them.

When a person acts as surrogate as well as egg donor, known as a traditional surrogacy, clinics in Victoria won't assist with the sperm transfer. They did the transfer themselves at home; and alternated days using both fathers' sperm.

Shortly after their first attempt, Carla told the boys she was pregnant over dinner at a restaurant, with the help of wait staff who delivered a wrapped parcel. Inside was a positive home pregnancy test.

"It felt right," says Simon. "Like everything had been leading to that."Carla said the pregnancy was nothing like what she went through with her three girls. She didn't bond with this baby in the same way.

"The whole joy of the pregnancy was about bringing happiness to these guys rather than having the outcome of having a new baby for yourself," she said. "I wasn't thinking of names or decorating nurseries or any of those things that you normally do when you have a baby."

And the couple were there every step of the way. They went to every antenatal appointment, got a copy of every ultrasound. When the baby moved, Carla would send them videos. "We discussed early on that we would be as apart of this as we possibly could," says Andy.

After the birth, staff at Box Hill Hospital had arranged two rooms side by side - one for the boys, and one for Carla - where they stayed for two days. Carla spent time with Adaline every day for the first week of her life, which helped as her hormones adjusted after the pregnancy, she said.

A recent survey of 150 members of a private Australian Facebook group for surrogates shows more than half are carrying for couples they previously did not know. It also found that more than one third of surrogates were carrying babies for gay male couples.

One in 10 surrogates, like Carla, donated their own eggs as well as carrying the baby. Carla has donated eggs to eight couples, both gay and heterosexual. All eight have had babies and two have gone on to have another two. There's plans for four more siblings next year. She keeps in touch with all of the families.

Her children will grow up knowing Adaline as a cousin of sorts. More than a friend but not like a sibling.

Being a surrogate is not right for everybody, Carla says. And trust, the trio agrees, is the most important ingredient when making a baby. "We were treating it as if we were a marriage of three for a while," laughs Carla.

They're planning to give Adaline a sibling next year. "She's just so perfect," says Simon, "you can't stop at one."